Schematic Diagram

Here’s simple FM receiver circuit for a simple superregenerative FM radio. It is sensitive, selective, and has enough audio drive for an earphone. These designs generally have low component counts, however the design or my construction have been far from simple.

FM Radio Receiver Circuit Layout
Because this is a superregenerative design, component layout can be very important. The tuning capacitor, C3, has three leads. Only the outer two leads are used; the middle lead of C3 is not connected. Arrange L1 fairly close to C3, but keep it away from where your hand will be. If your hand is too close to L1 while you tune the radio, it will make tuning very difficult.

Winding L1
L1 sets the frequency of the radio, acts as the antenna, and is the primary adjustment for super-regeneration. Although it has many important jobs, it is easy to construct. Get any cylindrical object that is just under 1/2 inch (13 mm) in diameter. I used a thick pencil from my son’s grade school class, but a magic marker or large drill bit work just fine. #20 bare solid wire works the best, but any wire that holds its shape will do. Wind 6 turns tightly, side-by-side, on the cylinder, then slip the wire off. Spread the windings apart from each other so the whole coil is just under an inch (2.5 cm) long. Find the midpoint and solder a small wire for C2 there. Mount the ends of the wire on your circuit board keeping some clearance between the coil and the circuit board.

A tuning knob for C3

C3 does not come with a knob and I have not found a source. A knob is important to keep your hand away from the capacitor and coil when you tune in stations. The solution is to use a #4 nylon screw. Twist the nylon screw into the threads of the C3 tuning handle. The #4 screw is the wrong thread pitch and will jam (bind) in the threads. This is what you want to happen. Tighten the screw just enough so it stays put as you tune the capacitor. The resulting arrangement works quite well.

FM Radio Receiver Circuit Adjustment
If the radio is wired correctly, there are three possible things you can hear when you turn it on: 1) a radio station, 2) a rushing noise, 3) a squeal, and 4) nothing. If you got a radio station, you are in good shape. Use another FM radio to see where you are on the FM band. You can change the tuning range of C3 by squeezing L1 or change C1. If you hear a rushing noise, you will probably be able to tune in a station.

Try the tuning control and see what you get. If you hear a squeal or hear nothing, then the circuit is oscillating too little or too much. Try spreading or compressing L1. Double check your connections. If you don’t make any progress, then you need to change R4. Replace R4 with a 20K or larger potentiometer (up to 50K). A trimmer potentiometer is best. Adjust R4 until you can reliably tune in stations. Once the circuit is working, you can remove the potentiometer, measure its value, and replace it with a fixed resistor. Some people might want to build the set from the start with a trimmer potentiometer in place (e.g., Mouser 569-72PM-25K).

Interfere with fm radio signal is fun, if youre bored or no work, you can do at home, where neighbors , at school , or even near the transmitter. With the circuit above you can interfere with the speech signal in condenser microphone , and the signal will be issued by the circuit will then be received by FM radio receiver and a voice that we remove it before going out mixed with the signals emitted by radio FM transmitter.

Part List :

R1  = 4K7

R2  = 2K2

C1  = 1n5

C2  = 47pF

C3  = 33pF

L1  = Nikelin wire coil with a diameter 0,8 mm and 5mm in diameter wound coil 10 x

T1  = 2N3906

Mic= Condenser Microphone

Schematic  is suitable for use in radio tuner or FM radio receiver when it is assembled and ready for use. Where if the low gear power radio receiver, with the aid of power amplifier is less powerfull voice / hard to better and just right. For use hios  speakers , use a low-power , because power amplifier has only the power output of 2 X 5 Watt stereo power amplifeir with impedance of 4 Ohm. Working on a minimum voltage of 4.5 Volts and maximum of 16Volt. Use the correct voltage supply - really have been filtered out in order to improve the performance of these power amplifiers.